This invention relates to web feed control devices and, more particularly, to devices that control the lateral position of a narrow continuous web that is fed longitudinally.
Many medical, chemical and biological diagnostic tests and assays for laboratory and home use have been reduced to an optimally simple routine: immerse a test strip or stick into a liquid, and observe the change in color of the test strip or stick to read the results of the test. Tests that formerly required days of laboratory work may now be carried out in seconds, with a reliability factor that exceeds former, more time-consuming methods. Generally speaking, the strips or sticks (hereinafter, "strips") comprise long, narrow pieces of paper, plastic, or similar sheet material that carry carefully formulated combinations of highly specific reagents, reactants, or assay compounds.
The individual reactants that comprise a particular test or assay may be embodied in respective lamina which are applied to the base strip. These lamina are formed of thin web material in which the reactant is dispersed in a concentration that is precisely controlled. Often the thin web material is a thin film having little structural strength and a low ratio of weight to surface area. As a result of such factors, these thin films may present serious problems in handling, particularly by automated fabrication machinery.
A common fabrication technique for test strips is to fabricate cards of base material, and to laminate a combination of thin film strips extending laterally across each card. Because the thin film strips are carriers for the respective reactants, it is crucial that the thin film strips be placed precisely and reliably in the same locations on each card, so that the interactions of the reactants are facilitated in a manner that does not vary from card to card. Each card is then slitted longitudinally into a plurality of strips, each strip bearing the same combination of all the thin film strips.
Due to the delicate nature of some of these thin film lamina, it can be difficult to feed the lamina from a supply reel onto a base card at a precise position. Conventional feed rollers may tear the film or abrade the surface, and side guides may fray the edges. The prior art is deficient in apparatus designed to deliver a delicate thin film longitudinally while precisely locating the edges of the thin film in a lateral direction.